1. Field of the Invention
The present invention relates to an estimation method for a film having the optical anisotropy due to the alignment of molecules, for example, a liquid crystal alignment layer and the like which provides the initial orientation to the liquid crystal molecules in a liquid crystal display device.
2. Description of the Related Art
The crystal rotation method ( described by T. J. Scheffer and J. Nehring in Journal of Applied Physics, Vol. 48, pp. 1783, 1977) has been widely employed as an optical method of measuring an angle that liquid crystal molecules in an antiparallel cell make with the reverse of a substrate. In this method, with the linearly polarized light incident on the sample, the optical retardation(phase shift) of the transmitted light which is generated through birefringence is measured as a function of the incident angle. On the other hand, instead of the direct measurement of the dependence of the polarization in the transmitted light on the incident direction, another measuring method in which an analyzer is placed behind a sample and the quantity of light transmitted through the analyzer is monitored as a function of the incident angle is also widely utilized.
However, the above-mentioned conventional techniques have the following problems as pointed out, for example, by K.-Y. Han et al. in Japanese Journal of Applied Physics, Vol. 32, pp. L1242-1244, L277-279 1993.
That is, because the liquid crystal is held between a pair of glass substrates, the refraction at the substrate causes a shift in the incident position of the light on the liquid crystal section, as the incident angle is changed. As the place through which the light passes within the liquid crystal is varied, the polarization of the transmitted light directly reflects the variance in thickness of the liquid crystal layer with the place, which hinders the accurate measurements. The incident angle of the light on the sample is usually changed by rotating the sample, and thus the relative position between the incident light and the transmitted light also changes, accompanying with the sample rotation. As a result, in order to carry out an accurate polarization measurement of the transmitted light, it is necessary for the positions of an analyzer and the like to be adjusted according to the thickness, the material and the rotation angle of the sample and the measuring efficiency of this method becomes low.
In light of the above problems, an object of the present invention is to provide a method of measuring a liquid crystal pretilt angle which determines a liquid crystal pretilt angle by setting the linearly polarized light incident on a liquid crystal sample and measuring the polarization of the transmitted light thereof; wherein:
said linearly polarized light is normal to the surface of the liquid crystal sample in incidence; and
by rotating said liquid crystal sample within plane, the dependencies of the amplitude ratio of said transmitted light as well as the optical retardation of said transmitted light on the azimuth of the liquid crystal sample with respect to the polarization direction of the incident light are measured and thereby the pretilt angle of said liquid crystal sample is determined.
Another object of the present invention is to provide a method of measuring a liquid crystal pretilt angle which determines a liquid crystal pretilt angle by setting the linearly polarized light incident on a liquid crystal sample and measuring the polarization of the transmitted light thereof; wherein:
having passed through a polarizer, said linearly polarized light is normal to the surface of the liquid crystal sample in incidence; and
by rotating said polarizer within plane, the dependencies of the amplitude ratio of said transmitted light as well as the optical retardation of said transmitted light on the azimuth of the liquid crystal sample with respect to the polarization direction of the incident light are measured and thereby the pretilt angle of said liquid crystal sample is determined.
Another object of the present invention is to provide a method of measuring a liquid crystal pretilt angle which determines a liquid crystal pretilt angle by setting the linearly polarized light incident on a liquid crystal sample and measuring the polarization of the transmitted light thereof; wherein:
having passed through a polarizer and a xc2xd-wave plate, said linearly polarized light is normal to the surface of the liquid crystal sample in incidence; and
by rotating said xc2xd-wave plate within plane, the dependencies of the amplitude ratio of said transmitted light as well as the optical retardation of said transmitted light on the azimuth of the liquid crystal sample with respect to the polarization direction of the incident light are measured and thereby the pretilt angle of said liquid crystal sample is determined.
Another object of the present invention is to provide an equipment of measuring a liquid crystal pretilt angle; comprising:
a light source;
a polarizer which polarizes the emitted light from said light source;
a holder which holds a liquid crystal sample as an object of the measurement;
a mechanism to rotate said holder within plane;
a means for measuring, with the light having passed through said liquid crystal sample, the amplitude ratio of said transmitted light as well as the optical retardation of said transmitted light; and
a means for determining a liquid crystal pretilt angle from said measured polarization.
Another object of the present invention is to provide an equipment of measuring a liquid crystal pretilt angle; comprising:
a light source;
a polarizer which polarizes the emitted light from said light source;
a mechanism to rotate said polarizer within plane;
a holder which is placed behind said polarizer and holds a liquid crystal sample as an object of the measurement;
a means for measuring, with the light having passed through said liquid crystal sample, the amplitude ratio of said transmitted light as well as the optical retardation of said transmitted light; and
a means for determining a liquid crystal pretilt angle from said measured polarization.
Another object of the present invention is to provide an equipment of measuring a liquid crystal pretilt angle; comprising:
a light source;
a polarizer which polarizes the emitted light from said light source;
a xc2xd-wave plate placed behind the polarizer;
a mechanism to rotate said xc2xd-wave plate within plane;
a holder which is placed behind said xc2xd-wave plate and holds a liquid crystal sample as an object of the measurement;
a means for measuring, with the light having passed through said liquid crystal sample, the amplitude ratio of said transmitted light as well as the optical retardation of said transmitted light; and
a means for determining a liquid crystal pretilt angle from said measured polarization.
In the method measuring a liquid crystal pretilt angle according to the present invention, the incident angle of the light with respect to the sample surface is constant and the optical path within the liquid crystal layer does not change during the measurement. Therefore, a deterioration in accuracy, resulting from non-uniformity of the liquid crystal layer thickness, which is a problem for the conventional methods, does not occur. Furthermore, in measuring the polarization of the transmitted light, unlike in the conventional methods, no adjustment of the detector position is required to accompany the rotation of the liquid crystal sample. The measurement can be made, while the detector is kept in a fixed position, which enables a rapid measurement. The polarization of the transmitted light may be calculated in terms of 4xc3x974 matrices with anisotropic dielectric constants xcex5e and xcex50, the pretilt angle xcex8 and the liquid crystal layer thickness d. Values of the pretilt angle xcex8 and the liquid crystal layer thickness d may be determined, then, through the optimization to fit the dependencies of the polarization of the transmitted light on either azimuthal direction of the sample or that of the polarized light which are obtained from the actual measurements.
Further, an equipment of measuring a liquid crystal pretilt angle according to the present invention has such an arrangement as described above that can carry out the above-mentioned method of measuring a liquid crystal pretilt angle favourably.
As described above, in the present invention, the incident angle of the light with respect to the sample surface is constant and the optical path within the liquid crystal layer does not change during the measurement. Therefore, a deterioration in accuracy, resulting from non-uniformity of the liquid crystal layer thickness, which is a problem for the conventional methods, does not occur. Furthermore, in measuring the polarization of the transmitted light, unlike in the conventional methods, no adjustment of the detector position is required to accompany the rotation of the liquid crystal sample. The measurement can be made, while the detector is kept in a fixed position, which enables a rapid measurement.